Wikipedia:Reference desk/Archives/Science/2007 September 17

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1 September 17

[edit] September 17

[edit] Recycling plants

I was wondering if you could point me in the right direction online as to where I can educate myself about recycling plants. I would be extremely grateful! thank you —Preceding unsigned comment added by 195.250.91.198 (talk) 00:05, 17 September 2007 (UTC)

What are you interested in recycling ? Metals ? Plastic ? Paper ? StuRat 00:48, 17 September 2007 (UTC)

You might try Materials recovery facility and Recycling. At first I thought the OP wanted to know about how to recycle his azaleas, and was a bit confused. -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 00:54, 17 September 2007 (UTC)

Recycling azaleas? Look at composting. -- 22:26, 17 September 2007 (UTC)

[edit] Rotating liquids

My kid is doing a project for an upcoming science fair, and I was thinking about helping her build something like this:

It looks cool and it's more original than a baking soda volcano, so I like it :) Would basically any two non-mixing substances work (I assume they have to have different densities)? Like cooking oil and water? Any other suggestions? How fast would it have to rotate? I guess you could experiment to find that out (depending on the amount of fluid, I'm assuming), but some equations would be neat. Me and my offspring would be very grateful and if she wins a prize or something, you're all getting barnstars :) Thanks in advance! 83.249.113.29 01:16, 17 September 2007 (UTC)

Dunno about the physics, but the fluids are easy: I believe it's traditional to use mineral oil and water in all such non-mixing-fluids gadgets. You can use any old water-based food coloring to give the water a pretty color, and/or a nonpolar dye for the mineral oil. --Steve Summit (talk) 01:35, 17 September 2007 (UTC)

1. Remember the rule "like dissolves like." i.e. Nonpolar substenses will not disolve/mix with polar substenses. (yes, in other words) 2.(see below). A pratical use for this is that a parabola will focus light, so if one of the liquids were mercury, you could have a realy big mirror, like for a telescope. (sombody did this once) 3. when a liquid is spun, the surfice will become a parabola, just like in the photo. a parabola can be expressed mathamaticly 4. you will get a parabola no matter what speed it would be spun at, but the greater the speed, the deeper the curve. (one could also do a study about rotation speed and curve steepness/depth) 5. Youre welcome. hacky 03:51, 17 September 2007 (UTC)

On the topic of reflective parabolic liquid surfaces, see liquid mirror, mercury mirror. TenOfAllTrades(talk) 12:33, 17 September 2007 (UTC)

In the context of the original question, I think we should say that a real mercury mirror is not a suitable candidate for a science fair project because of the dangers of mercury poisoning (although building a demo model with a safe liquid would be fine). Gandalf61 13:30, 17 September 2007 (UTC)

The speed you'd need to rotate it would depend on the ratio of the densities of the two liquids and the diameter of the tank. But I'd guess that a really low speed would work quite well. I would grab an old bicycle with a set of Derailleur gears. The bicycle frame should simplify the mechanical construction. I'd attach the pedal end to the tank and the back-wheel end to an electric screwdriver (those have fairly low speeds and lots of torque - so probably better than an electric drill. The bearings on the pedal end are strong enough to support a person standing on the pedal - so it should be plenty strong enough to support the weight of the water tank. Placing the chain onto the smallest gear first would give you the slowest speed of rotation - which will give the drill the extra torque needed to get the tank started - and also be slow enough not to slosh liquid everywhere. If you find you need more speed, you can move the derailleur up to a larger gear wheel. If you need less speed, you could put the back wheel back on the bike and use an electric drill with the chuck pressed against the tyre to spin the thing REALLY slowly. Tell us how it goes! We need pictures! SteveBaker 13:56, 17 September 2007 (UTC)

One thing to watch out for is creating an emulsion. If you accelerate the liquids too quickly, you will end up with a mess that looks like a bottle of salad dressing which has just been shaken. The layers will eventually settle out, but probably not until well after it stops moving. StuRat 02:57, 18 September 2007 (UTC)

With a big tank like the one in the picture, that's unlikely to be a problem - the tank will need a LOT of torque to get it moving, so a violent startup would be unlikely - and even when it is started, the tank will be spinning but the liquid inside will mostly be stationary. I agree though that with a much smaller tank, and some nice wine vinegar replacing the water, you might have just built the world's greatest French dressing maker...which might still make for a good science project! SteveBaker 13:57, 18 September 2007 (UTC)

Stu might be thinking of a stationary round Plexiglas tank where a paddle at the bottom is used to spin the liquids, in which case if the paddle is very thin and spinning at a high enough speed then it might be possible to use egg whites instead of water and produce mayonnaise instead of salad dressing, oh wait, mayo is salad dressing, what am I thinking? Clem 02:31, 23 September 2007 (UTC)

[edit] looking for the name of something

what would the "study of the relationship between the mind and the body" be called? I know it will end in "olgy" but I don't think it is psycology. —Preceding unsigned comment added by 76.19.185.11 (talk) 03:47, 17 September 2007 (UTC)

It depends on what you mean by "mind." If you're talking about the physical aspects of the brain, that would be covered by neurology. If you're talking about "that which does the thinking," that would be psychology. If you want to know the relationship between mental processes and physical/chemical interactoins in the brain/body, you're thinking of neuropsychology. If you want to know the true distinction between the mind and the brain, you'll have to look towards philosophy. Someguy1221 05:04, 17 September 2007 (UTC)

[edit] Could science genetically engineer an organism which can survive for extended periods of time in outer space?

Let’s say a being which can work and move in outer space for about 36 hours without need for special gear, and for even longer on terrain at almost zero Kelvin, with very thin atmosphere. 5 hurdles as far as I can see.

1. Zero pressure. Could be insuperable, I thought, but then we have sea bed creatures that live in pressures hundreds of time greater than at sea level. If they can do it, why could we not design a creature that can do with one less than us. Just a case of having a very sturdy casing with pluggable orifices and insulation for eyes etc.

2. Zero Gravity. Big problem with terrestrial animals, but fish exist in what is virtually zero gravity.

3. Cold. Well insulated skin would be needed, perhaps like a polar bear’s. Also the type of anti-freeze found in salamander blood.

4. No air. Whales can dive for hours without air. Organism would have to be able to super-saturate blood and organs with oxygen, to be released gradually.

5. Damage by cosmic rays. Genetic code would need to be double coded with extra checking bits to overcome radiation damage.

All in all, I can’t see huge problems here. In the next 50 years we will have the technology to do this. Why do I ask? Because this being, which I see as some kind of beaver with tentacles, will have HUMAN DNA, it will be our homogenobased descendant (my coinage). Let’s face facts. We will not conquer space and other planets looking like tourists from Sydney. Extreme conditions will require radical modifications to the morphology and genetics of the human organism. Yet virtually all the commentators on humans in space ignore the fact that what is happening now in Genetics is far far more important than progress in the rockets, ray guns and robots fields that so entrance sci fi addicts to the exclusion of all else. What say you? Are we going to be carrying bits of earth environment around with us forever, like deep sea divers, or am on the right track? A new man who can live in extreme conditions with a minimum of special gear. Myles325a 05:28, 17 September 2007 (UTC)

But the whole point of sending humans to space is that it is actual humans that go. If you're not going to send actual humans, why not just send robots of some type and cut out all the mucking around (hell, they could even carry some human DNA with them if you really want the DNA out there)? Or am I missing your point? --jjron 07:01, 17 September 2007 (UTC)

1) Good luck. 2) This one is easy, humans can already operation in zero gravity. 3) Near 0 Kelvin, seriously? Consider that there is almost no motion at such temperatures, so you couldn't do it with anything resembling a known life form. The insulation required would be incredible, just keeping something at 70 Kelvin for long periods requires an extremely well built thermos. And antifreezes don't work even at 200 Kelvin; I've confirmed this myself. 4) Yes, giant air supply is possible somewhere...in theory. Not that genetic engineering is at the point where we can add new organs to an organism, aside from making mice grow human ears. But I guess if you're starting with something that can already do that, good for you. 5) Biologists still haven't fully figured out how organisms naturally control their genes, so genome-wide alterations aren't even in the scope of speculation yet.
Now, I hate to have been a pessimist, but it's simply that a lot of people have a distorted view of what genetic engineering can do. Genes aren't the blueprints for the body that the press and popular culture often make them out to be. Individual genes just code for chemicals, and it is individual chemicals that are the targets of current genetic engineering projects. Someguy1221 08:25, 17 September 2007 (UTC)

Cold isn't that big of a short-term problem because there's not much anything to leak heat to. However, over the long term...it's a huge problem. -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 08:43, 17 September 2007 (UTC)

Note that making organisms that are resistant to even extremely high doses of radiation is possible—nature has already done it with Deinococcus radiodurans. D. radiodurans will survive a dose of radiation a hundred times that which would kill a human being. Nicknamed 'Conan the Bacterium', it is also resistant to heat, cold, dehydration, vacuum, and acid in addition to intense radiation. Of course, scaling that up to anything bigger than a bacterium is an exercise left to the reader. TenOfAllTrades(talk) 12:29, 17 September 2007 (UTC)

I don't see why you'd bother. It's much simpler to provide a life-support suit of some kind. I could certainly imagine a suit that would keep you safe in vacuum/zero-g for 36 hours - existing space-suits can keep you alive for 8 to 9 hours - quadrupling that shouldn't be too big of a challenge. The insanely low temperatures you talk about are not relevent in a vacuum. The whole concept of temperature is meaningless in a vacuum - deep space doesn't have a temperature because there is nothing there to measure the temperature of! A big problem may well be shedding heat - not retaining it. The creature you envisage would probably be totally crippled in a 'normal' environment - this seems like a ridiculously drastic step compared to wearing a space-suit. If you insist on thinking about it this way, far from being a "beaver with tentacles" (where the heck did THAT idea come from?!) - that seems like the worst possible design! If you are really concerned about unprotected survival in low temperature and vacuum, you'd want something close to being spherical so as to minimise surface area and maximise the ability to contain internal pressure sufficiently to prevent liquids from boiling...tentacles are definitely out! But operating in almost absolute zero environments is just not going to happen. SteveBaker 13:39, 17 September 2007 (UTC)

I, for one, support our new tentacled space beaver overlords. --Sean 14:48, 17 September 2007 (UTC)

Image:TentacledSpaceBeaver.jpg

All hail!

See pantropy, and I think you really want to read a book called The Seedling Stars. --Reuben 16:54, 17 September 2007 (UTC)

Quite do-able, but it might be more than 50 years. Edison 01:47, 18 September 2007 (UTC)

We probably have life forms now that could survive those conditions, like some seeds, I imagine. Getting life forms that can actually do anything besides hibernate under those conditions is entirely different, however. StuRat 02:46, 18 September 2007 (UTC)

[edit] double acting gasoline engines

hey friends i ve designed a double acting gasoline engine.i really want to know that whether such engines r availaible.if not then it would be a great matter for me.

regards Reveal.mystery —Preceding signed but undated comment was added at 06:22, 17 September 2007 (UTC)

There are an awful lot of alternative configurations that have been invented already. The Bourke engine might be what you are thinking of - or perhaps Split Cycle Engine, or Twingle engine, or the Stelzer engine. I strongly recommend looking at all of the links in the table at the bottom of those pages that contains links to dozens of articles to alternative kinds of gasoline engine. SteveBaker 13:22, 17 September 2007 (UTC)

[edit] "violotion" of law of conservation of energy ?

According to special relativity the mass of any object or particle increases with increase in speed . is'nt that a violation of law of conservation of energy ? because we know mass is a form of energy .

Except that you have to supply an object with that same increase in energy to make it speed up. Conservation achieved! Someguy1221 08:11, 17 September 2007 (UTC)

Actually it's more common now not to talk of mass changing at all, but to modify the formula for energy. If you want to think of mass energy equivalence, it is easier to think of the extra kinetic energy acting to cause the extra mass, rather than vice versa. Cyta 08:52, 17 September 2007 (UTC)

The concept of invariant mass (as distinct from relativistic mass) is probably useful to mention here. TenOfAllTrades(talk) 13:53, 17 September 2007 (UTC)

Yes. When physicists talk about "mass" in a relativistic context, they almost invariably mean invariant mass. Relativistic mass is relatively uncommon. In popular books and articles, it's the other way around, and this leads to a lot of confusion. I believe the physicists switched over some time around 1950, as it was gradually decided that invariant mass is a more useful concept. So now physicists don't often talk about mass changing with velocity. --Reuben 16:50, 17 September 2007 (UTC)

[edit] Field Maple

I have some large field maples (20m) in my garden one of which needs to be felled. They are old slow growing trees (the garden has been cultivated since the thirteenth century). The tree has a good straight trunk but I want to know whether the timber will weather outside well (e.g. can I season it and then use it for raised beds). All I can find on google is the same couple of texts repeated endlessly about it being good for musical instruments, mallet heads and bird's eye veneers, not the weatherability of large planks. --BozMo talk 09:03, 17 September 2007 (UTC)

Generally, maple is too expensive for that kind of usage - that's probably why there is no information about weathering outdoors. You might want to investigate whether you can sell the trunk and use the money to buy some (much cheaper) pressure-treated lumber which will last for a very long time. SteveBaker 12:55, 17 September 2007 (UTC)

I'm curious: why are you taking them down? Are they unhealthy? --Sean 14:54, 17 September 2007 (UTC)

Only one. Planted too close to other trees (or they were planted close to it) and is dying back from the top. There are more magnificent ones I won't touch. --BozMo talk 19:17, 17 September 2007 (UTC)

[edit] Heron

A Heron like bird

At the risk of sounding hopelessly naive, I would like to ask: what bird is this ? and whether this photograph I took, may be added to the relevant article. I would appreciate any help. I am sorry in advance if it is not too useful. :) Vijeth 09:42, 17 September 2007 (UTC)

Do we have any Asian ornithologists here? It should be emphasized that the picture was taken in Hyderabad. TenOfAllTrades(talk) 13:56, 17 September 2007 (UTC)

I think I'd start looking under cranes Richard Avery 21:31, 17 September 2007 (UTC)

Or ask at Wikipedia talk:WikiProject Birds.--Jude. 13:58, 19 September 2007 (UTC)

[edit] aerodynamics

can an aeroplane be stand still at a place like a helicopter?203.94.231.74 10:42, 17 September 2007 (UTC)

Depends on the aeroplane. Most cannot but see Harrier Jump Jet as an example. —Preceding unsigned comment added by BozMo (talk • contribs) 10:48, 17 September 2007 (UTC)

In general, not unless they've been specially designed to do so (as the Harrier was) - but aside from that, with the right conditions (if the wind speed is equal to the air-speed of the aircraft), a plane will appear to be standing still from the point of view of someone on the ground. Hence, some aircraft have a low enough stall speed that they can 'hover' in fairly modest winds. Also, aside from the Harrier, there are also the Tiltrotor craft that blur the line between a fixed-wing plane and a helicopter. SteveBaker 12:52, 17 September 2007 (UTC)

Other designs that allow fixed-wing aircraft to hover and/or land vertically are tiltwing and the (not very practical) tailsitter design. All designs are based around the requirement to smoothly change the direction of thrust between horizontal in normal flight and vertical in a hover. Our article on VTOL gives a good overview. Gandalf61 12:59, 17 September 2007 (UTC)

I wonder if a jet with enough horsepower to accelerate straight up, and thrust vectoring for control could point upwards and hover for a bit? That would be a neat trick. --Sean 15:00, 17 September 2007 (UTC)

I believe Sukhoi has created models of aircraft that could do just that. StuRat 02:19, 18 September 2007 (UTC)

Actually - quite a lot of modern fighters have the power to do that. You only have to be able to accellerate at >1g which lots of modern planes can do. The problem for hovering with those aircraft is that as the airspeed over the control surfaces drops you start to lose control over the beast - if you are literally hover, you have no control whatever over the aircraft. Depending on what happens next, this can be rather dangerous. If the aircraft has thrust vectoring, then a modicum of control is still possible - but whilst they proudly show it at air shows, this is hardly a practical manouver! SteveBaker 13:49, 18 September 2007 (UTC)

Prototypes of the flying flapjack could hover vertically if the wind was just right. Someguy1221 18:44, 17 September 2007 (UTC)

You might also check out the F-35. -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 23:55, 17 September 2007 (UTC)

[edit] Symmetry

What is the likelihood of getting a wart in the exact same spot on each index finger? Clem 12:08, 17 September 2007 (UTC)

Warts are caused by a viral infection through the skin. If you spend time with your two index fingers pushed against each other symmetrically the chances might be quite high... --BozMo talk 12:11, 17 September 2007 (UTC)

When I was a child, I had a small plantar wart in the exact center of my fingerprint whorl. I have always considered this to be non-random, so maybe there's something to it. --Sean 15:03, 17 September 2007 (UTC)

Reminds me of ol' Dan Tucker, who died with a toothache in his heel :-) --Trovatore 18:09, 17 September 2007 (UTC)

Haha, I just noticed that a plantar wart is foot-only by definition! OK: I had a thing that looked just like a plantar wart in my finger. :) --Sean 19:26, 17 September 2007 (UTC)

There is said to be a psychological aspect to warts, so if your brain makes a connection between two symmetrical parts of your body then that might just cause a new wart. Just a wild (and only slightly educated) guess. DirkvdM 08:51, 18 September 2007 (UTC)

[edit] Naming of electronic components

What is the basis of naming electronic components?
for eg:1N 4001 etc? Its kind of a homework question. But googling 'naming of electronic components' wasn't very helpful (yet). For zener diodes I think that the name incorporates the breakdown voltage; right? the page Electronic_component does'nt seem to have it. Still searching If someone knows a link or something where it is discussed in detail It would be helpful. 59.93.41.117 14:15, 17 September 2007 (UTC)

I think JEDEC were responsible for categorising and maybe naming in conjunction with the manufacturers--88.111.135.162 15:46, 17 September 2007 (UTC)

[edit] railway semaphores

Why did I.K. Brunell device and built semaphores on the GWR that indicate clear in a downward position? This construction is more expensive and more prone to failure than the everywhere else used signalling by which the arm is pointing upward to indicate clear. wally. 82.173.141.164 14:46, 17 September 2007 (UTC)

"Why" is a tough question to ask when it comes to GWR, I've found. :) Brunel also thought a 7' rail gauge was a good idea too. But yes, the Lower Quadrant signalling does seem like it could fail to a dangerous condition. Saturn 5 20:39, 20 September 2007 (UTC)

[edit] Mama seagull - will she recognise her own offspring?

It's getting to about that time of year when this year's fledgling gulls are cut loose by their parents to fend for themselves. Just wondering - will the mother/father gull treat her/his 'grown up' offspring any differently to any other gull when if/when they encounter each other in the future - or will they be seen as just more gulls to squabble with over food and perches? I know that magpies tend to stick together in family groups but it's quite hard to tell with gulls - as they never really obviously interact with each other in a friendly social manner (they just kinda stand near each other if they don't want to fight). --Kurt Shaped Box 15:03, 17 September 2007 (UTC)

Well, you're our resident seagull expert, I doubt if anyone here knows more about them than you. Maybe you should mark some seagull families (dye, perhaps ?) so you can identify them and see if they react differently in subsequent years. If you were in the US, you could probably get a million dollar grant to do so. :-) StuRat 02:09, 18 September 2007 (UTC)

You *could* ring the gulls in question and observe their interactions. That sounds like something that someone may have already studied... --Kurt Shaped Box 16:46, 18 September 2007 (UTC)

[edit] steam engine advantages at high altitude

"Steam locomotives are especially advantageous at high elevations as they are not adversely affected by the lower atmospheric pressure. This was inadvertently discovered when steam locomotives operated at high altitudes in the mountains of South America were replaced by diesel-electric units of equivalent sea level power. These were quickly replaced by much more powerful locomotives capable of producing sufficient power at high altitude."

In reading that I thought it to be dubious for these reasons Studying the statement that asserted that steam engines are advantageous at high altitude is a partial truth. While it does satisfy Carnot's cycle by having high pressure steam coming into the engine, and exhausting the steam at very low pressure. (thermodynamically efficient) it does not take into account the combustion of the fuel used to heat the water to make the steam. Any engine that derives its power from chemical energy (diesel, jet, gasoline) requires a certain amount or ratio of fuel to air to operate properly. Recall that the supercharger was used in war to maintain sea level pressure so that aircraft would maintain power at all altitudes (turbochargers). The locomotive style boiler has no means of forced induction and as a result the air is "rare" and thus the sociometric ratio is compromised. I think this issue should be addressed. Spencer —Preceding unsigned comment added by 199.17.91.22 (talk) 15:10, 17 September 2007 (UTC)

This sounds like something that should be addressed on the talk page of whichever article you are referring to. If you return to that article and click on the "discussion" tab at the top, you will be able to address your concerns to an audience that is more specifically interested in and informed on the topic. --LarryMac | Talk 17:44, 17 September 2007 (UTC)

That assumes that the availability of oxygen is going to be a limiting factor for a locomotive at any reasonable altitude. Is that a reasonable assumption?

In a (non-turbo, non-supercharged) internal combustion engine, the amount of fuel that can be burnt (and therefore the amount of energy that can be extracted) per unit time is a function of the total amount of fuel and air that fits in the cylinders and engine revs (more revolutions per second means more combustion cycles). As you decrease the atmospheric pressure, the amount of air that the engine ingests per cycle falls, reducing the amount of fuel that can be burnt and limiting the available energy. The maximum speed of the engine is limited by its mechanical strength, so you can't restore the lost power by cranking the engine faster.

In a steam locomotive, coal is shovelled into the firebox, where it is burnt in available air at atmospheric pressure. Air is continuously drawn into the firebox, and combustion products are continuously vented through the smokestack. As long as it's possible to draw air through the firebox drafts then the coal will continue to burn. (In other words, at any reasonable atmospheric pressure, the coal in the firebox will be able to suck in as much air as it needs at any given time. Contrast this with an internal combustion engine, where each volume of air has to be drawn in mechanically.) Will the combustion of each lump of coal proceed more slowly with the lower partial pressure of oxygen? Possibly—but you can get around that by adding a bit more coal (increased combustion surface area) to maintain the same total amount of heat per unit time. TenOfAllTrades(talk) 21:35, 17 September 2007 (UTC)

What's wrong with an ATOMIC powered steam engine. No requirements for minimum oxygen levels, just boil the water to make lots of steam. 202.168.50.40 00:56, 18 September 2007 (UTC)

Thanks that really clarified it. I failed to take into account the draft produced and the constant supply of air to support combustion of the coal. Spencer —Preceding unsigned comment added by 69.42.233.219 (talk) 04:42, 18 September 2007 (UTC)

[edit] Freaking out. (Bio/Med Q.)

I'm freaking out. I clean my desk and other surfaces in my room with alcohol which seems to 96% ethanol and i presume 4% methanol. When its all evapourated the room usually has a fairly strong odour to it. Is the amount of methanol in the air enough to do any damage to my body? i probably only use a small amount of the liquid each time and its only %4 anyway and by the time its dispersed amongst my room it probably woulndt be in any concentration that would do any noticeable damage... Right??? any im only exposed to it for 5minutes until diffused out windows/other rooms ect and no longer noticeable. I know this is probably silly but thanks anyway. Lolfalroflealal 15:31, 17 September 2007 (UTC)

Standard alcohol formulations such as this are 95ish% ethanol and the rest is primarily water not methanol (but only you have the actual bottle to read the ingredients on this particular product). See azeotrope to learn why 95% is a convenient concentration. DMacks 17:02, 17 September 2007 (UTC)

Wikipedia does not give medical advice. I have never heard of a cleaning/sterilizing solution containing so much methanol that its vapors do harm. That said, it couldn't hurt to leave a window open. Plasticup ^T/C 20:27, 17 September 2007 (UTC)

Contrary to popular belief, ethanol itself has an odour (from Ethanol: "Ethanol, like most short-chain alcohols, is flammable, colorless, has a strong odor, and is volatile."). When using a significant amount of it (say in cleaning), it can get quite overpowering, especially if the room is poorly ventilated. -- 22:26, 17 September 2007 (UTC) —Preceding unsigned comment added by 72.33.121.200 (talk)

Where are you? The alcohol that I use for cleaning is isopropyl. —Tamfang 00:54, 18 September 2007 (UTC)

I'm told that ethanol is a better disinfectant. I think isopropanol is just cheaper. But I have to agree, I doubt the other 4% is methanol. That's something that would probably be written on the bottle. Someguy1221 03:35, 18 September 2007 (UTC)

don't worry about it, remember, ask yourself this question when in fear of methanol: what is the antidote to methanol poisoning? Ethanol. have a beer, imagine how the ethanol is competitively using up the same enzymes that methanol would fuck with, and relax. —Preceding unsigned comment added by 12.217.199.246 (talk) 02:05, 18 September 2007 (UTC)

If you want to avoid methanol poisoning, just take a shot of ethanol ;O
Mrdeath5493 03:47, 18 September 2007 (UTC)

Alcohol based cleaning fluids sometimes contain ethanol and a surfactant such such benzyl alkonium sulponate.. Read the label it should tell you what exactly is in it - ie if there is methanol or not and any possible dangers - it is possible that the fumes themselves are making you high and paranoid..87.102.7.192 09:46, 18 September 2007 (UTC)

[edit] Cosmological Redshift and the conservation of energy

Consider a photon created shortly after the era of recombination. At the time its wavelength would likely be about 966 nm, corresponding to an energy of 1.28348270 eV. Now say that it travels along, not interacting with anything, for 13.5 billion years or so. During that time the Universe expands significantly and the photon's wavelength is increased to 1,900,000 nm. It now has only 6.5255*10^-4 eV of energy. So it lost 1.28283015 eV without any interactions. When I asked my physics professor to explain this he replied "under the most general forms of general relativity, energy is not conserved". True? False? Plasticup ^T/C 20:51, 17 September 2007 (UTC)

Strange but true! In fact, there's no good way to define the total energy of the universe in general relativity! --Reuben 20:55, 17 September 2007 (UTC)

Break out the Stress-energy-momentum pseudotensor! It's controversial and some people think it's hand-wavey, but it lets you conserve something like energy in general relativity. Damned if I know how to use it, though. See also "Is Energy Conserved in General Relativity? for a summary and some good references. (The nutshell answer from that site is "In special cases, yes. In general -- it depends on what you mean by 'energy', and what you mean by 'conserved'.") TenOfAllTrades(talk) 21:14, 17 September 2007 (UTC)

What does "hand-wavey" mean ? StuRat 01:49, 18 September 2007 (UTC)

Lacking rigor. Which seems inappropriate here, since it's a rigorous idea, just not a generally covariant one. -- BenRG 02:08, 18 September 2007 (UTC)

Some people find the lack of general covariance...disturbing. TenOfAllTrades(talk) 03:27, 18 September 2007 (UTC)

Conveniently, we have an article on handwaving. TenOfAllTrades(talk) 03:27, 18 September 2007 (UTC)

The photon appears to be gaining gravitational potential energy. I don't know if that's the same amount as it's losing from decreasing wavelength, though. — Daniel 23:01, 18 September 2007 (UTC)

[edit] Understanding Motion

My question is:

How do I calculate the velocity and accelaration of a free falling object if the object is 45 meters above the ground and free falls to the earth?

Have a look at the Acceleration article, and then Newton's law of universal gravitation. Probably what you are looking for though is Equation of motion. — RJH (talk) 22:40, 17 September 2007 (UTC)

If it's 'free falling' and we are neglecting air resistance, the only force is gravity - so the acceleration must be 'g' (the accelleration due to Standard gravity) which is about 9.8ms^-2 (although it varies a bit depending on where you are on the earth). The equation you need from the classical equations of motion is: v²=u²+2as (where u is the initial velocity, v is the final velocity, a is the accelleration and s is the distance travelled). We know that s=45m, u=0ms^-1 (assuming the object was stationary at the start), a=g=9.8ms^-2 - so substituting into the equation and taking the square root of both sides, we get v=sqrt(2x9.8x45) which gives us roughly v=29.7ms^-1. SteveBaker 13:36, 18 September 2007 (UTC)

[edit] Comparator input capacitance

Anyone know (or make a guess at) the input capacitance of the SE521 comparator? The data sheet doesn't say.--88.111.135.162 23:22, 17 September 2007 (UTC)

That's surprising, but you're certainly correct: it doesn't say. But we can infer, based on the speed of the part and the fact that the inputs are bare transistor bases, that it can't be much, a few pF at most. If you had an LCR meter, a network analyzer, or a TDR, you could measure it. Or you could just call NXP/Philips and ask them.

Atlant 12:46, 18 September 2007 (UTC)

I do have a meter that can measure down to about 1pF but Im not sure if the part should be energised when making the measurement as I suspect the capacitance will vary with the state of bias of the input stage. Any thoughts?--88.111.135.162 13:55, 18 September 2007 (UTC)

Yes, energized, but LCR meters don't like applied DC voltages so put a DC blocking capacitor in series with the meter and the DUT. You can either make the blocking capacitor largish (say, 1nF) so its effects are immaterial or you can do the series-capacitor calculation to mathematically remove its effects later. Either way, connect the test circuit, short the LCR meter's inputs, energize the test circuit (so the blocking cap charges), and ONLY THEN unshort the LCR meter's inputs and make your measurement.

Atlant 15:38, 18 September 2007 (UTC)

Looking at other comparator data for fast comparators, it seems to be about 3-4pF. I'm gonna take this as a guess and trim my compensator for best looking i/p w/f on the input pin somehow.--88.111.135.162 15:08, 18 September 2007 (UTC)

Sounds like a good plan! Don't forget, though, that your 'scope probe has a pF or ten as well.